Frame metadata for kernel modules is only read once at startup

[rockdaboot]

Kernel modules can be loaded/unloaded at any time. But currently, the agent only reads in the list of modules at startup. The agent does not send frame metadata for modules that are loaded after agent start. Frame information for modules that are unloaded are kept in agent memory, consuming memory unnecessarily.

TBD

• Find a way to detect loading/unloading of kernel modules.
• Read module frame metadata on-demand.
• Drop the initial reading of kernel modules.

[christos68k]

Looks like dup of #172 (I'd close #172 and keep this open)